The present invention relates to a method of selectively depositing metal nanoparticles onto conductive substrates such as carbon nanotubes, and more particularly, to a method which allows electroless deposition of metal nanoparticles onto carbon nanotubes and other conductive substrates without the need for a reducing agent.
Carbon nanotubes have been demonstrated to possess excellent electronic properties, good chemical stability, and a large surface area. These unique properties make carbon nanotubes very useful for supporting metal nanoparticles in many potential applications, including advanced catalytic systems, electrochemical sensors, and highly efficient fuel cells. Consequently, functionalization of carbon nanotubes with metal nanoparticles is becoming increasingly important.
Several methods currently exist for attaching metal nanoparticles onto carbon nanotubes. Examples include chemical binding through DNA double helix linkages, electrochemical deposition, electroless deposition, and physical/chemical deposition on carbon nanotubes, with and without surface activation. Electroless deposition is of particular interest because its simplicity could potential facilitate large-scale production of nanotube-nanoparticle hybrids. However, general applications of electroless deposition have been limited due to the fact that only metal ions having a redox potential which is higher than that of a reducing agent or carbon nanotubes can be reduced into nanoparticles on the nanotube support. As a single-walled carbon nanotube (SWNT) has a redox potential of +0.5 V vs. SHE (standard hydrogen electrode), it is impossible to reduce Cu2+ (Cu(NO3)2/Cu, +0.340 V vs. SHE) or Ag+ (Ag(NH3)2+/Ag+0.373 V vs. SHE) for deposition onto single walled carbon nanotubes via a galvanic displacement reaction without the aid of a reducing agent.
Accordingly, there is still a need in the art for an improved method of depositing metal nanoparticles onto conductive substrates such as carbon nanotubes.